Polymeric fibers and filaments are used to make a variety of products including yarns, carpets, woven fabrics, and nonwoven fabrics. As used herein, polymeric fibers and filaments are referred to generically as polymeric strands. Filaments mean continuous strands of material and fibers mean cut or discontinuous strands having a definite length.
It is often desirable that polymeric strands and articles made with polymeric strands be soft and strong. This is particularly true for nonwoven fabric and articles made with nonwoven fabric. Nonwoven fabrics are typically used to make garments such as work wear, medical apparel, and absorbent articles. Absorbent products made with nonwoven fabric include infant care items such as diapers, child care items such as training pants, feminine care items such as sanitary napkins, and adult care items such as incontinence products.
Nonwoven fabrics are commonly made by meltspinning thermoplastic materials. Meltspun fabrics are called spunbond materials and methods for making spunbond materials are well-known. U.S. Pat. No. 4,692,618 to Dorschner et al. and U.S. Pat. No. 4,340,563 to Appel et al. both disclose methods for making spunbond nonwoven webs from thermoplastic materials by extruding the thermoplastic material through a spinneret and drawing the extruded material into filaments with a stream of high velocity air to form a random web on a collecting surface. For example, U.S. Pat. No. 3,692,618 to Dorschner et al. discloses a process wherein bundles of polymeric filaments are drawn with a plurality of eductive guns by very high speed air. U.S. Pat. No. 4,340,563 to Appel et al. discloses a process wherein thermoplastic filaments are drawn through a single wide nozzle by a stream of high velocity air. The following patents also disclose typical meltspinning processes: U.S. Pat. No. 3,338,992 to Kinney; U.S. Pat. No. 3,341,394 to Kinney; U.S. Pat. No. 3,502,538 to Levy; U.S. Pat. No. 3,502,763 to Hartmann; U.S. Pat. No. 3,909,009 to Hartmann; U.S. Pat. No. 3,542,615 to Dobo et al.; and Canadian Patent Number 803,714 to Harmon.
Spunbond materials with desirable combinations of physical properties, especially combinations of strength, durability, and softness have been produced, but limitations have been encountered. For example, in some applications, polymeric materials such as polypropylene may have a desirable level of strength but not a desirable level of softness. On the other hand, materials such as polyethylene may, in some cases, have a desirable level of softness but a not a desirable level of strength.
In an effort to produce nonwoven materials having desirable combinations of physical properties, nonwoven fabrics comprising multicomponent strands such as bicomponent strands or multiconstituent strands such as biconstituent strands have been developed.
Methods for making bicomponent nonwoven materials are well-known and are disclosed in patents such as Reissue 30,955 of U.S. Pat. No. 4,068,036 to Stanistreet, U.S. Pat. No. 3,423,266 to Davies et al., and U.S. Pat. No. 3,595,731 to Davies et al. A bicomponent nonwoven fabric is made from polymeric fibers or filaments including first and second polymeric components which remain distinct. The first and second components of multicomponent strands are arranged in substantially distinct zones across the cross-section of the strands and extend continuously along the length of the strands. Typically, one component exhibits different properties than the other so that the strands exhibit properties of the two components. For example, one component may be polypropylene which is relatively strong and the other component may be polyethylene which is relatively soft. The end result is a strong yet soft nonwoven fabric.
Multiconstituent strands are similar to multicomponent strands except that one component does not extend continuously along the length of the strands. The noncontinuous component is typically present as a multitude of discrete polymer segments connected by the other polymeric component.
Although conventional bicomponent and biconstituent nonwoven fabrics have desirable levels of strength, durability, and softness, there is still a need for nonwoven materials which are made with polymeric strands and have particular combinations of strength, durability, and softness. Furthermore, there is a need for garments made with nonwoven materials having particular combinations of strength, durability, and softness.